Electrical Insulation Systems for
Thermoplastic Encapsulated Coils and Components

With better productivity, lower overall costs, and fewer environmental concerns, high performance thermoplastics are increasingly being used to replace thermosets in the encapsulation of motor stators, solenoids, and transformers.

Many of these applications require IEC/UL Electrical Insulation System recognitions. However, in the case of encapsulated coils and components, the EIS used are tested to more rigorous requirements than systems used for applications that are open to the atmosphere. These systems for encapsulated applications have to take into account that gases may be sealed in with a coil under an encapsulation layer, for example. As a result, to gain a IEC/UL recognition is very difficult.

At DuPont, UL testing is performed with bifilar wound solenoids that are encapsulated with thermoplastics in our laboratory. After the encapsulated solenoids are approved by a UL engineer, they are tested as follows:

• Heat Aging
  High temperature: 3-day cycle
  Middle temperature: 7-or 14-day cycle
  Low temperature: 28-day cycle
  
  
• Cold Shock
  Hold until stabilized at -20°C
  
  
• Mechanical Stress
  Vibration at 60 Hz for 3 min
  
  
• Moisture Exposure
  48 hr at 92-100% RH room temperature
  
  
• End of Life Test
  Check for shorted turns.
  Ground insulation dielectrically stressed to ground at two times the rated voltage plus 1000 V for 10 min.

For a 600 V system, the test voltage is 2200 V. The test protocol requires that the low temperature have a geometric mean time to end-of-life of at least 5000 hr. The high temperature must have a geometric mean time to end-of-life of at least 100 hr. System evaluations are carried out according to UL 1446.

Using this test procedure, DuPont has obtained UL recognition for UL 1446 Listed Insulation Systems for Encapsulated Systems operating at a 600 V maximum. They are as follows:

DuPont and EIS | EIS Explained | DuPont Materials
Selecting the Right EIS | Encapsulated Components | Wire Substitutions